Disease

Mottled, blotchy leaves: could it be a plant virus?

Last reviewed September 2026 · written from Cooperative Extension and university horticulture references — see how we source data

Illustration of squash-family leaves with a blotchy light-green and yellow mosaic pattern and puckered, distorted edges, with small aphids on the underside of a leaf.

What you’re seeing

Leaves show a blotchy, mottled pattern of light and dark green (sometimes yellow), often paired with distorted, curled, or narrowed leaf shape and stunted overall growth; fruit can be misshapen or mottled too.

Could it be something else?

Nutrient deficiencyEven yellowing of older leaves, or yellow between neat green veins, rather than an irregular light-and-dark patchwork - see yellowing lower leaves.

Herbicide driftNew leaves cupped, twisted or narrow and strap-like soon after nearby lawn or weed spraying, often on several kinds of plant at once.

Spider mitesFine pale speckling across the leaf, often with faint webbing underneath, rather than larger light and dark blotches.

Likely causes

Ranked most common first.

Aphid or other insect transmission. Most common garden mosaic viruses (cucumber mosaic virus, tobacco mosaic virus, and others) spread mainly through aphids feeding on an infected plant and then moving to a healthy one.
Contaminated tools or hands. Some viruses, notably tobacco mosaic virus, spread easily on pruning shears, hands, or even tobacco products, without needing an insect at all.
Infected seed or transplants. A small number of viruses can be carried in seed or arrive already present in a nursery transplant.

How to fix it

Confirm the pattern is genuinely mottled/blotchy rather than a solid yellowing (which points to a nutrient deficiency) or interveinal yellowing (which points to a mineral deficiency) - both are far more common than virus and both are fixable.
There is no cure for a confirmed viral infection - remove and discard the whole plant to stop it from acting as a source for aphids to spread to neighboring plants.
Control aphids proactively on remaining plants, since they are the primary spreader for most common vegetable-garden viruses.
Disinfect pruning tools with rubbing alcohol between plants, especially in a bed where any plant has shown virus symptoms.
Avoid handling tobacco products before working with tomato-family plants if tobacco mosaic virus is suspected, since it survives readily on hands.

Common mistakes

Leaving an infected plant in place 'to see what happens'. Aphids feeding on it carry the virus to healthy plants.
Saving seed from infected bean plants, since some bean viruses are carried in the seed.
Handling tomatoes and peppers straight after using tobacco products, which can spread tobacco mosaic virus.
Spraying fungicide. Viruses are not fungi, and no garden spray cures them.

When and where it shows up

Symptoms usually appear on new growth a week or more after aphids have been active, most often in early to mid summer. Cucumber mosaic virus infects cucumbers, squash, melons, peppers, tomatoes, spinach and many weeds. Tobacco and tomato mosaic viruses mainly attack the tomato family, and bean common mosaic affects beans and is carried in the seed.

Preventing it next time

Control aphids early in the season, buy certified disease-free seed and transplants, and disinfect tools between plants when working through a bed.

Questions gardeners ask

Can a plant recover from mosaic virus?

No. Once a plant is infected it stays infected. Remove it to protect the rest of the garden.

Is fruit from a virus-infected plant safe to eat?

Yes. Plant viruses do not infect people, though the fruit may be mottled, bumpy or misshapen.

How can I be sure it is a virus?

The pattern - irregular light and dark mottling with distorted new growth - is a strong clue, but a lab test through your local extension service is the only way to be certain.

Are there resistant varieties?

Yes. Many cucumber and squash varieties are listed as tolerant of cucumber mosaic virus, and many tomatoes carry resistance to tobacco and tomato mosaic viruses (labelled TMV or ToMV). Controlling aphids helps too.

Related crops

Cucumber →